The present invention relates to a battery pack constituted using secondary batteries which are formed accommodating electricity generating elements within a soft external case, in order to achieve reduction in size, weight and thickness that is required for battery power sources of portable information equipment such as mobile telephones or mobile computers.
The ratio represented by the batteries in the volume and weight of portable information equipment such as mobile telephones or mobile computers is considerable, and it is no exaggeration to say that batteries hold the key to reduction in size, weight and thickness of portable information equipment.
Flat-shaped lithium ion secondary batteries are employed in order to respond to such demands for reduction in size, weight and thickness of portable information equipment; however, it is anticipated that lithium polymer secondary batteries may provide secondary batteries capable of further reductions in weight and thickness. In particular those formed by accommodating electricity-generating elements in the form of a laminated sheet within an external casing are effective in realizing reductions in weight and thickness.
In secondary batteries of high energy density such as lithium-based secondary batteries, in order to prevent deterioration or damage to the battery by overcharging, over-discharging, or excessive discharge current etc., the use of a battery protective device constituted using a protection circuit or PTC etc. is indispensable. Such is accommodated in a battery pack case together with the secondary battery to constitute a battery pack.
However, swelling of the external casing occurs when the secondary battery undergoes expansion of the electrode plates due to repeated charging/discharging and/or changes over time, or when gas is generated by decomposition of the electrolyte due to causes such as being left at high temperature in a fully charged condition. When such a condition is generated in the secondary battery accommodated in the pack case, the swelling of the secondary battery is communicated to the pack case, producing changes in the external dimensions of the pack case. In the case of miniature portable equipment such as mobile telephones, the battery pack faces the constituent elements of the equipment with only a slight intervening gap, wherefore changes in the external dimensions of the pack case affect the equipment. In particular, in the case of a secondary battery wherein the external casing is formed by soft material such as laminated sheet, expansion of the electrode plates or generation of gas immediately produces swelling of the external casing, and this produces swelling of the pack case, changing its external dimensions.
Also, in the case of secondary batteries of a construction in which a group of laminated electrode plates constituted by laminating a plurality of positive and negative electrode plates is accommodated in a soft external casing made of for example laminated sheets, the restraining force whereby the external casing holds the positive and negative electrode plates in their prescribed positions is weak, so positional displacement of the electrode plates can easily occur when subjected to shock or vibration, giving rise to the problem of damage such as internal short-circuits or disconnections being easily produced. Also, even in the case of a secondary battery of a construction in which electrode plates in which positive and negative electrode plates are coiled are accommodated in a soft external casing, damage occurs due to disconnections etc. produced by movement of the electrode plates. Also, since the laminated sheets are formed by disposing a resin layer on both sides of a metallic layer, if a secondary battery is displaced within the pack case by vibration or shock, the resin layer is destroyed by contact with metallic members arranged within the pack case, giving rise to short-circuiting between the metallic members and metallic layer.
An object of the present invention is to provide a battery pack in which reduction in size, weight and thickness are achieved by solving the problems in a battery pack employing a secondary battery in which a soft material is used for the external casing.
According to a first aspect of the present invention, a battery pack wherein a secondary battery formed in flat plate shape by accommodating electricity generating elements within an external casing formed of soft material is accommodated in a pack case is characterized in that a face on one side of said pack case, facing a flat plate face of said secondary battery, is formed as a resiliently deformable face that deforms resiliently corresponding to changes in thickness of the secondary battery, while the face on the other side is formed as a rigid face consisting of a rigid element.
With such a construction, although it might be feared that if the secondary battery constituted by accommodating electricity generating elements within a soft external casing such as a laminated sheet suffered expansion of the electrode plates constituting the electricity-generating element, such expansion would immediately be communicated to the external casing, producing swelling of the pack case with adverse effect on the equipment thanks to the formation of one face of the pack case opposite the battery by a resiliently deformable face, the increase in thickness of the resiliently deformable face of the battery pack takes place uniformly without swelling in specific locations, so abnormal deformation is not produced in the external shape of the battery pack, and there is thus no possibility of adverse effect on the equipment due to swelling of the battery pack. Even in the case where the aforesaid secondary battery is constituted by electricity generating elements using electrode plates of a coiled construction in which the positive and negative electrode plates are coiled, when this is formed into flat plate shape, a condition is produced in which the electrode plates are laminated in the thickness direction, so that this is the same as the case of the laminated construction in which a plurality of positive and negative electrode plates are laminated; thus swelling of the electrode plates results in a uniform increase in the thickness of the secondary battery. Thus, whether the electrode plates are of laminated construction or of coiled construction, the benefit of the resiliently deformable face is obtained.
According to a second aspect of the present invention, a battery pack wherein a secondary battery formed in flat plate shape by accommodating electricity generating elements within an external casing formed of soft material is accommodated in a pack case is characterized in that both faces of said pack case opposite flat plate faces of said secondary battery are formed as resiliently deformable faces that deform resiliently corresponding to changes of thickness of the secondary battery, and their peripheral portion is supported by a rigid element surrounding the side faces of the secondary battery.
With the above construction, in the event of swelling of the electrode plates constituting the electricity-generating element, since the thickness of the battery pack as a whole increases in uniform fashion due to the resilient deformation of the resiliently deformable faces formed on both faces of the pack case, abnormal deformation of the external shape of the battery pack cannot occur. Even when the aforesaid secondary battery is constituted by electricity generating elements employing electrode plates of coiled structure in which positive and negative electrode plates are coiled, when this is formed in flat plate shape, a condition in which the electrode plates are laminated in the thickness direction is produced, so that, just as in the case of the laminated construction in which a plurality of positive and negative electrode plates are laminated, swelling of the electrode plates results in uniform increase in thickness of the secondary battery. Consequently, whether the electrodes are of laminated construction or coiled construction, the benefit of the aforesaid resiliently deformable face is obtained.
According to a third aspect of the present invention, a battery pack wherein a secondary battery formed in flat plate shape by accommodating electricity generating elements within an external casing formed of soft material is accommodated in a pack case is characterized in that the internal dimension in the thickness direction of said pack case is formed smaller than the thickness of the secondary battery, and both faces or one face opposite a planar face of said secondary battery are formed as resiliently deformable faces that deform resiliently corresponding to changes of thickness of the secondary battery.
With this construction, since the battery is accommodated in a pack case that is formed with internal dimension in the thickness direction that is smaller than the thickness of the battery, the resiliently deformable face is resiliently deformed, and a condition is produced in which pressure is constantly applied in the compression direction to the battery accommodated therein, by this stress. Expansion of the battery that is constantly subjected to this pressure in the compression direction is suppressed, enabling the thickness change of the battery pack to be reduced. Even when the aforesaid secondary battery is constituted by electricity generating elements employing electrode plates of coiled structure in which positive and negative electrode plates are coiled, when this is formed in flat plate shape, a condition in which the electrode plates are laminated in the thickness direction is produced, so that, just as in the case of the laminated construction in which a plurality of positive and negative electrode plates are laminated, swelling of the electrode plates results in uniform increase in thickness of the secondary battery. Consequently, whether the electrodes are of laminated construction or coiled construction, the benefit of the aforesaid resiliently deformable face is obtained.
According to a fourth aspect of the present invention, a battery pack wherein a secondary battery formed in flat plate shape by accommodating electricity generating elements within an external casing formed of soft material is accommodated in a pack case is characterized in that one face or both faces of this pack case opposite a flat plate face of said secondary battery is formed by a resiliently deformable face that deforms resiliently corresponding to changes of thickness of the secondary battery, a peripheral part being formed that projects to a prescribed height from resiliently deformable face at the periphery or on both sides of this resiliently deformable face.
With this construction, even if the resiliently deformable face swells up on the inside of the peripheral part, this does not result in change in the external dimensions of the battery pack, and so there is no effect on the equipment in which the battery pack is loaded due to changes in external shape. Consequently, the projecting height of the peripheral part is set so as not to be less than the maximum amount of swelling of the resiliently deformable face produced by swelling of the battery. Even when the aforesaid secondary battery is constituted by electricity generating elements employing electrode plates of coiled structure in which positive and negative electrode plates are coiled, when this is formed in flat plate shape, a condition in which the electrode plates are laminated in the thickness direction is produced, so that, just as in the case of the laminated construction in which a plurality of positive and negative electrode plates are laminated, swelling of the electrode plates results in uniform increase in thickness of the secondary battery. Consequently, whether the electrodes are of laminated construction or coiled construction, the benefit of the aforesaid resiliently deformable face is obtained.
According to a fifth aspect of the present invention, a battery pack wherein a secondary battery and a battery protection device constituted by providing a circuit board formed with at least a protective circuit to protect the secondary battery are accommodated within a pack case formed in flat shape, a positive electrode lead and negative electrode lead leading from said secondary battery being connected to external input/output terminals that are provided on the pack case on the other side of said battery protecting device is characterized in that electricity generating elements of said secondary battery is accommodated within an external casing which is sealed by welding the peripheral parts of a pair of laminated sheets, a positive electrode lead and negative electrode lead being led from the weld-sealed side, said battery protection device being arranged on the side of this secondary battery where said positive electrode lead and negative electrode lead are led out.
With this construction, since the positive electrode lead and negative electrode lead of the secondary battery are led out from one weld-sealed side of a laminated sheet constituting an external casing, a battery protection device being arranged on this side where the leads are led out, a simple construction is achieved with the minimum distance of the connection between the secondary battery and battery protection device, and the number of constituent members and processing steps can be reduced and the thickness of the battery pack can easily be decreased.
With this construction, since the circuit board has its planar direction parallel with the flat plate face direction of the secondary battery, and at least part of the weld-sealed portion of the external casing is arranged in an overlapped position, small size and thickness of the battery pack can be achieved by accommodating the battery protection device in a pack case of small thickness and providing an accommodating space in respect of the welded seal.
By means of a construction in which the battery protection device is arranged offset to one side in the thickness direction within pack case, the positive electrode lead being connected with a positive electrode connection member connected to a circuit board and a negative electrode connection member and negative electrode lead being connected at a position offset in the other direction of the thickness direction within the pack case, a weld-sealed portion of the battery being arranged between this lead connection position and battery protection device, insulation between the lead connection portion and the battery protection device can be ensured by interposing the weld-sealed portion therebetween, even though the lead connection position is arranged on the battery protection device.
By arranging an insulating member between at least the weld-sealed portion of external casing and battery protection device, incidents of the weld-sealed portion of the external casing which is arranged overlapping the battery protection device coming into contact with the circuit board etc. and coming into contact with a conductive location in a metallic layer by destruction of the resin of the laminated sheet when subjected to vibration or impact can be prevented.
By a construction in which the battery protection device is provided with a PTC element, this PTC element being formed in plate shape, the direction of its planar face being parallel with the flat plate direction of the secondary battery and at least part of the weld-sealed portion of external casing being arranged in an overlapped position, generation of wasted space within the thin pack case can be avoided, making it possible to reduce the size and thickness of the battery pack.
According to a sixth aspect of the present invention, a battery pack wherein a secondary battery formed in flat plate shape by accommodating electricity generating elements formed by a laminated sheet is accommodated in a pack case is characterized in that said pack case comprises a planar portion facing both flat plate faces of said secondary battery and a plurality of wall face parts facing the side faces of this secondary battery, said planar part and wall face parts being constituted so as to restrict the position of accommodation of the secondary battery in the pack case.
With this construction, since the planar faces of the secondary battery face planar parts of the pack case on both sides, and each side face is accommodated within the pack case by positional location in a condition surrounded by wall faces of the pack case, there is no possibility of the secondary battery being displaced within the pack case when subjected to impact etc., so damage to the battery due to impact can be prevented even for the case of a secondary battery in which the electricity-generating element is accommodated in an external casing formed by a laminated sheet.
According to a seventh aspect of the present invention, a battery pack wherein a secondary battery is accommodated in a pack case divided into a top case and bottom case in the thickness direction of the secondary battery formed in flat plate shape, a battery accommodating space of internal dimension corresponding to the thickness of the secondary battery being formed when the two cases are mated by bringing into abutment bonding parts respectively formed on both cases, the battery pack being thereby integrated by bonding the two cases by said bonding parts, is characterized in that fitting-in parts are formed that effect mutual fitting-in between both cases such as to maintain a positionally located condition by abutment between said bonding parts when the two cases are mated with said pack case accommodating the secondary battery, a secondary battery formed in flat plate shape being accommodated in this pack case by accommodating an electricity generating element within a soft external casing.
In the above construction, the secondary battery accommodating electricity generating elements within a soft external casing, compared with a battery in which the electricity-generating element is accommodated within a rigid external casing such as a metallic casing, does not have a fixed and uniform thickness, on account of the softness of the external casing, and exhibits resilience in respect of outside pressure due to the pouring in of electrolyte into the casing. When this is accommodated in a pack case formed with a battery accommodating space of internal dimension corresponding to the thickness of the secondary battery, when the top case and bottom case are mated, due to the thickness of the secondary battery, it may happen that, even when these are pressed together, the bonding portions of the two cases cannot be brought together and positional location cannot be achieved. With the construction described above, by forming the faces of the top case and/or bottom case opposite the planar faces of the battery as resiliently deformable faces, and forming fitting-in parts between the two cases, when the top case and bottom case are pressed together so as to bring the bonding parts of the two cases into contact, any thickness error of the secondary battery is absorbed by deformation of the aforesaid resiliently deformable faces, and any possibility of the two cases springing back from a positionally located condition due to resilient recoil of the secondary battery is obviated by the fitting together of the two cases by these fitting-in parts. Consequently, even if the two cases are unified by bonding by bonding means such as ultrasonic welding, since a contacting condition is maintained between the bonding parts, bonding of a pack case accommodating a secondary battery whose thickness is not fixed and uniform can be achieved in a stable fashion.
In the above construction, by adopting a construction wherein wall faces are formed surrounding the side faces of the secondary battery at the periphery of the battery accommodating space, bonding parts being formed near to the outside of these wall faces, the strength of the wall faces where the outer case is bonded to the bonding surface is increased, and deformation of the wall faces due to impact is prevented, so damage to the secondary battery due to deformation of the wall faces is prevented.
According to an eighth aspect of the present invention, a battery pack wherein a secondary battery formed in a rectangular flat plate shape by sealing electricity generating elements within an external casing formed by laminated sheet is accommodated within a pack case is characterized in that, within said pack case, there are formed in said pack case a position restricting location that restricts the accommodation position of said secondary battery and a space-forming location that provides a space between itself and the secondary battery.
With the construction described above, by restricting the accommodation position of the secondary battery within the pack case, the position-restricting location formed within the pack case fixes the secondary battery in position within the pack case, thereby preventing movement of the secondary battery when this is subjected to impact or shock. Also, the position-restricting location that abuts the planar surface prevents expansion of the electrode plates by applying tensioning pressure in the direction of lamination of the electrode plates. Also, since the space-forming location forms a space between itself and the secondary battery, when swelling is generated in the external casing due to generation of gas, the swelling of the soft external casing formed by the laminated sheet is accommodated in the space provided by the space-forming location, so that the swelling of the external casing cannot cause changes in the external dimensions of the pack case.
In the above construction, by suitably forming position-restricting locations and space-forming locations in respect of the secondary battery on the inside face of the pack case facing the planar faces of the secondary battery, expansion of the electrode plates is suppressed by the position-restricting locations restricting the position of accommodation of the secondary battery in the pack case and applying tensioning pressure thereto, and swelling of the external casing can be absorbed by the space-forming locations.
In a secondary battery of the above construction, a group of laminated electrode plates obtained by laminating a plurality of positive and negative electrode plates is accommodated within a soft external casing. With a secondary battery of this laminated type, positional offset in the laminated plates tends to occur when these are subjected to vibration or impact, but, by the position-restricting locations applying tensioning force from both sides, displacement of the electrode sheets is prevented by positional a restriction of their side faces.
By forming position-restricting locations so as to surround at least the four corners of the secondary battery on the inside face of the pack case, facing the side faces of the secondary battery, the secondary battery of rectangular shape is restricted in position by the position-restricting locations at the four corners, so displacement of the laminated electrode plates cannot occur even when these are subjected to impact or vibration, and internal short-circuiting etc. due to displacement of the electrode plates can thus be prevented.